The preovulatory gonadotropin surge initiates the final process of follicular maturation that culminates in ovulation of an expanded cumulus-oocyte complex (COC) and formation of the corpus luteum (CL). One essential step elicited by the gonadotropin surge required for successful follicular maturation is the expression of specific transcription factors. However, our knowledge of the identity and regulatory actions of LH-induced key transcription factors remains very limited. Recent studies from our laboratory and others shed light on a small family of nuclear transcription factor, Core binding factor (CBF), as a key transcriptional regulator involved in periovulatory processes. CBF is composed of two subunits;DNA binding alpha-subunit encoded by one of Runx1, Runx2, and Runx3 genes and non-DNA binding beta-subunit, CBF2. To be functional, RUNX proteins need to be dimerized with CBF2. Our preliminary data showed the rapid induction of CBF components (Runx1, Runx2 and CBF2) by the LH surge in periovulatory follicles. Using an in vitro model, we further demonstrated that CBFs (RUNX1/CBF2 and RUNX2/CBF2) regulate the expression of periovulatory genes that are known to be critical for COC expansion, ovulation, and luteinization. Moreover, our pilot study revealed that inhibition of RUNX activity blocked COC expansion in vitro. Based on these novel findings, we hypothesized that CBFs are key transcriptional regulators necessary for successful COC expansion, ovulation, and luteinization. Homozygous null mutation of genes for CBF components in mice results in early lethality and, consequently, fails to define the function of CBFs in the ovary. The additional challenge in demonstrating the physiological importance of CBFs in vivo is the overlapping expression of Runx1 and Runx2 and their functional redundancy in periovulatory follicles. To circumvent this problem, we propose to establish a novel transgenic mouse model in which CBFs are inactivated specifically in ovarian cells. This will be accomplished by deleting CBF2 in ovarian cells using Cre-lox technology. Since CBF2 is a binding partner for both RUNX1 and RUNX2, targeted deletion of CBF2 abrogates the activity of all CBFs (RUNX1/CBF2 and RUNX2/CBF2). Using this transgenic mouse model, we will test the hypothesis that targeted inactivation of CBFs results in defective COC expansion, ovulation, and luteinization by examining the ovarian phenotype of this mutant mouse (Specific Aim #1). Using this mutant mouse ovary, we will identify the genes downstream of CBFs in periovulatory follicular cells and begin to delineate the transcriptional regulatory pathways necessary for the final stage of periovulatory follicle development (Specific Aim #2). These studies will establish a genetically modified animal model not only to define the in vivo ovarian function of CBFs, but also to identify the transcriptional regulatory machinery that controls the periovulatory process. Information derived from this proposal will provide new insight into the mechanism(s) involved in COC expansion, ovulation, and CL formation. Gaining a thorough understanding of cellular/molecular mechanisms of the periovulatory process will lead to better diagnostic evaluation of ovarian pathology and facilitate the physiological manipulation of these processes to either promote or inhibit fertility. PUBLIC HEALTH RELEVANCE: The overall goal of the proposed study is to investigate how the LH surge induces the release of a mature egg from the ovary and corpus luteum formation, which are essential steps for female fertility. The current proposal focuses on determining the function of a small family of transcription factors, Core binding factors (CBFs) as key LH-induced mediators in these processes. Such knowledge can be applied for promoting and inhibiting these critical facets of ovarian physiology, thereby allowing us to better manage fertility, infertility, and ovarian-based disorders.